In order to produce drill holes in the ground or for the purpose of destroying and replacing pipelines placed in the ground, pile driver drilling devices are used, which have a percussion piston arranged inside the device that can be moved back and forth.
Pile driver drilling devices of this type have been exceptionally suitable for the trenchless placement of lines in the ground and for the replacement of pipelines in the ground by destroying and then replacing them. They require a change in direction in order to be able to produce, for example, blind holes, or in order to avoid the need for digging up a device restrained by an insurmountable obstacle in the ground, instead, being able to move out of the bore hole it already created by means of-reverse operation.
For a change in direction, numerous systems are known, all of which are based on the fact that the impact energy of the percussion piston, moving axially inside the housing of the device, is introduced into the housing of the device, not in the direction of advance, but in the opposite direction, with the aid of a rearward housing stop for the percussion piston. This takes place in a simple manner, whereby adjusting a control slide inside the housing of the device, whose control edges are displaced axially, determines the point at which the ventilation of the working space, located before the percussion piston in the area of the tip of the device, takes place. At that time the respective control edges are placed opposite the direction of advance, so that the working space is ventilated at a later point in time and, accordingly, the percussion piston with its rearward front surface impacts with a stop forming a rigid part of the housing.
The construction and mode of operation of the control slide vary greatly in practice. For example, the European Patent 484,839 describes a pile driver drilling device with a step pipe, extending into a rear working space of the percussion piston and forming a rigid part of the housing on which an axially adjustable control casing is mounted. Between the control casing and the housing wall is the axially guided percussion piston with its cover surrounding the rear working space.
In the interior of the control casing, between a stop on the operating air supply step pipe, and a collar of the control casing, a readjusting spring is located which, in cooperation with control air supplied via a channel parallel to the axis, sustains the control casing against the pressure of the operating air in the working space of the percussion piston when in its advance position.
If the interior of the control casing is ventilated, then the force resulting from the operating air inside the working space of the percussion piston exceeds the spring force opposing it, with the result that the operating air compresses the spring by moving the control casing into its rearward, or reverse position, from which position it can again return to its advance position with the aid of the control air and the readjusting spring.
With this changing of direction, it is a disadvantage that the percussion piston is guided directly on the control casing and that the readjusting spring is located in the interior of the control casing since the smallest diameter is therefore determined by the diameter of the readjusting spring. This restricts the outer diameter of the pile drilling device to a minimum value. An additional problem results when the spring breaks in the return position, which can easily occur during the great dynamic stress and the small amount of space, at which time a change in direction into the advance position, via the compressed air, is no longer possible. On the other hand, if the spring breaks in the advance position, the advance movement! automatically changes to the return reverse! position without the possibility of external control.
The axially moving control box is also in constant sliding contact with the interior wall of the piston. During increased friction, as occurs during contamination or insufficient lubrication, the control box can move back and forth since the slight forces for changing its direction are not sufficient for restraining the box axially. The same problem arises when an automatically driven pile driver drilling device locks up or bends, while passing through various soil layers inside the earth.
Finally, the control channel consists of two concentric pipes, requiring more radial space than when the control air is supplied through one or several radial bores. In particular, in the case of smaller devices, this is a great disadvantage since little space remains for exhaust air and air supply channels.